The Herpes Simplex Virus (HSV) is a virus that causes cold sores and genital herpes in humans. It is also sometimes referred to as human herpes virus. There are two types of the herpes simplex virus found in humans. Herpes Simplex 1 or HSV-1 is the virus that is responsible for causing cold sores. This is also known as oral herpes. The Herpes Simplex Virus 2 HSV-2 is the virus that is most responsible for genital herpes. Although HSV-1 can cause genital herpes, the majority of cases are cased by the HSV-2 virus.